PHLEBCEDESIS IN CHALTOPODA 



27 



Astacus and of Limulus, should be regarded as remnants of the 

 coelom, the bulk of which has been filled up by swollen blood- 

 vessels, leaving only epinephric and gonadial sacs in the Arthro- 

 poda, pericardial and gonadial sacs in the INIollusca. 



Some years later my assistant, Dr. Benham, now Professor in 

 Dunedin, New Zealand, described (Quart. Jour. Micr. Sci. xxxix. 

 1896) a condition of the blood-vessels in the Chajtopod Magelona, 

 which is parallel to that through which the vessels of ancestral 

 Molluscs and Arthropods must have passed. Phlebredesis is carried 



Dv. 



LexC 





■obL 



lattxt 



dor. y. JTV. 



ctrc 



Fio. 14.— Traxsverse Section of the Thoracic Region of the Ch.etopod Maoelona 

 TO show the swelliso of the Blood-vessels and consequent reduction of the 



CtELOM. 



D.v, dorsal vessel; G, gut; .V, nerve conl ; V.v, ventral vessel greatly swollen, 

 filled with a peculiar corpusculated blood ; lat.ext, lateral extension of the same ; cr>\ 

 coelom ; l.v, lateral vessel ; l.m, longitudinal muscles ; circ, circular muscles ; obi, 

 oblique muscles ; dor.v.m, dorso-ventral muscle. (After Benham.) 



to such a point in Magelona as to extinguish to a large extent 

 the proper ccelomic cavity (see Fig. 14). This observation seems 

 to be of importance as showing the tendency to Phleboedesis in 

 Chsetopods among the ancestors of which the ancestors of both 

 Mollusca and Arthropoda are in all probability to be sought. 

 When we remember further that in some Cha^topods the cells 

 which should form the blood-vessels and the blood, may actually 

 break up altogether and give rise to floating htemoglobinous 

 corpuscles with a total absence of blood-vessels (Glycera and 

 Capitellidse), we must admit that it is not surprising that the task 



